The Collaborative International Dictionary of English v.0.48:

Thar \Thar\, n. (Zool.)
   A goatlike animal (Capra Jemlaica) native of the Himalayas.
   It has small, flattened horns, curved directly backward. The
   hair of the neck, shoulders, and chest of the male is very
   long, reaching to the knees. Called also serow, and imo.
   [Written also thaar, and tahr.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

IMO
    n 1: the United Nations agency concerned with international
         maritime activities [syn: International Maritime
         Organization, IMO]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

IMO
       In My Opinion (slang, Usenet, IRC)


The Free On-line Dictionary of Computing (30 December 2018):

IMHO
IMAO
IMNSHO
IMO

    (From SF fandom via Usenet) In My Humble Opinion.
   Also seen in variant forms such as IMO, IMNSHO (In My
   Not-So-Humble Opinion) and IMAO (In My Arrogant Opinion).

   [Jargon File]

   (1998-09-24)