From The Collaborative International Dictionary of English v.0.48 :
buttoned-down \buttoned-down\ adj.
conservatively formal and businesslike in dress and manner.
Syn: button-down, conservative.
[WordNet 1.5]
a colorful character in the buttoned-down,
dull-gray world of business. --Newsweek
From WordNet (r) 3.0 (2006) :
buttoned-down
adj 1: unimaginatively conventional; "a colorful character in
the buttoned-down, dull-grey world of business"- Newsweek
[syn: button-down, buttoned-down, conservative]