爱华网relation和relationship都是解关系，很多时候可以互通，relationship比较讲情感上的关系，relation则比较讲工作上的关系。现在分析各个情况：
一、国与国的正式邦交一定用relations，注意这里一定要用复数。
1.Canadaand Britain have established diplomatic relations with NorthKorea.
2.Britainthreatened to break off diplomatic relations with theregime.
但国与国之间的关系则可以用relations（必须用复数）或relationship（可数名词），情感上的关系尤其会用relationship。
1.US-Chinese relations (OxfordDictionary)
2.We seekto improve relations between our two countries. (LongmanDictionary)
3.TheChinese President has said the China will maintain its traditionalfriendly relationship with Bangladesh.
4.thespecial relationship between Britain and the US (LongmanDictionary)
二、人与人之间的关系既可用relations（必须用复数）或relationship（可数名词）。relations通常是指工作上的关系，relationship通常是指情感上的关系。
1.Relations between workers and management aregenerally good. (Longman Dictionary)
2.I havequite a good relationship with my parents. (LongmanDictionary)
3.She hasa close relationship with her daughter. (LongmanDictionary)
三、物与物之间的关系既可用relation（countable anduncountable），也可用relationship（countable anduncountable）。两个字完全互通。bear no/little relation/relationshipto是一个固定词组，与…没有关系。
1.therelation between rainfall and crop yields (OxfordDictionary)
2.therelationship between poor housing and health problems (LongmanDictionary)
3.The feethey are offering bears no relation to the amount of work involved.(Oxford Dictionary)
4.Thelessons bear little relationship to the children's actual needs.(Longman Dictionary)
四、情侣关系用relationship（可数名词），性关系则是sexualrelationship（可数名词）。情爱的关系不用relation。
1.Shedoesn't really want a relationship with me. (LongmanDictionary)
2.She'shad a series of miserable relationships. (OxfordDictionary)
3.Are youin a relationship right now? (Longman Dictionary)
4.He'snever had a sexual relationship before. (LongmanDictionary)
五、有血缘关系的人=blood relation/bloodrelative（可数）
He couldbe the next-door neighbor, a friend, a blood relation. (LongmanCorpus)
六、其它:
劳资关系=labour relations/industrialrelations
1.acompany with good labour relations (Longman Dictionary)
2.Nationalization in the transport industriesproduced neither outstanding industrial relations nor employeecommitment. (Longman Corpus)
公共关系=public relations
1.publicrelations exercise是固定词组，指改善公关的工作。
2.Theproject has been disastrous for the bank in terms of publicrelations. (Longman Dictionary)
3.Newcastle manager Kevin Keegan looked upon thetournament as a public relations exercise rather than a moneymakingventure. (Longman Corpus)
4.Thetour was considered to have been a successful public relationsexercise. (Longman Corpus)
5.It hasbeen a public relations exercise for this week's by-elections.(Longman Corpus)
种族关系=racerelations
1.We needto do more to promote good race relations. (LongmanDictionary)
2.Community leaders are working to improve racerelations in the city. (Longman Dictionary)
3.Hawaiihas a tradition of good race relations. (LongmaeDictionary)
这三个关系都是用relations（必须用复数）。
Definitionsofsite1:
Relation:blood ties; cognation;common ancestry; consanguinity; family ties; kinship; line;relationship;
Relative:agnate; aunt; brother;brother-in-law; cognate; cousin; father-in-law; grand-aunt;grand-daughter; grandfather; grandmother;
grandson; grand-uncle; great-aunt; great-uncle; kinsman; kinswoman;kissing cousin; kissing kin; mother-in-law; near relation;
nephew; next of kin; niece; relation; sister; sister-in-law;stepbrother; stepfather; stepmother; stepsister;uncle;
Definitions of site2:
Relative：person connected byblood or affinity;strictly,one allied by blood;a relation;a kinsmanor kinswoman.
Relation:aperson connected by consanguinity or affinity; a relative; akinsman or kinswoman; a person related by blood ormarriage.
Relationship:the state ofbeing related by kindred, affinity, or otheralliance.
Kin: relatives;persons of the same family orrace.
下面这些，也很有意思，最简单的也是最实用的：
Father: onewho has begotten a child, whether son or daughter; a generator; amaleparent.
Mother: a female parent; especially, one ofthe human race; a woman who has borne achild.
Parent: onewho begets, or brings forth, offspring; a father or amother.
Grandfather:a father's or mother's father;an ancestor in the next degree above thefather or mother in linealascent.
Great-grandfather&great-grandmother: the father of one's grandfather or grandmother. And themother of one's grandfather orgrandmother.
Child:ason or a daughter; a male or female descendant, in the firstdegree; the immediate progeny of humanparents.
