Sentence:  <WSD>completist</WSD> - A dope who tries to have a complete collection in some line. The line may be as broad as having all the prozines ever published, or as narrow as collecting all the Golden Atom tales or all official correspondence during one's incumbency in some office. The trouble arises when the collector misses purchasing an issue (or fails to keep a carbon copy, or whatever), or when his ambitions extend back to a time before he started saving the stuff. Then he prowls the 2d-hand magazine shops, writes letters to everybody who mite know where a particular prize is, worries librarians and other public servants, and occasionally makes a marvelous find in some unexpected place and goes around rejoicing. 
Meaning of the word marked with <WSD> tags:  A collector who strives to obtain a complete collection of some type of thing.