Search Result for "obligatory": 
Wordnet 3.0

ADJECTIVE (2)

1. morally or legally constraining or binding;
- Example: "attendance is obligatory"
- Example: "an obligatory contribution"

2. required by obligation or compulsion or convention;
- Example: "he made all the obligatory apologies"



The Collaborative International Dictionary of English v.0.48:

Obligatory \Ob"li*ga*to*ry\, a. [L. obligatorius: cf. F.
   obligatoire.]
   Binding in law or conscience; imposing duty or obligation;
   requiring performance or forbearance of some act; -- often
   followed by on or upon; as, obedience is obligatory on a
   soldier.
   [1913 Webster]

         As long as the law is obligatory, so long our obedience
         is due.                                  --Jer. Taylor.
   [1913 Webster]


WordNet (r) 3.0 (2006):

obligatory
    adj 1: morally or legally constraining or binding; "attendance
           is obligatory"; "an obligatory contribution" [ant:
           optional]
    2: required by obligation or compulsion or convention; "he made
       all the obligatory apologies"