The Collaborative International Dictionary of English v.0.48:
Lookout \Look"out`\, n.
1. A careful looking or watching for any object or event.
2. The place from which such observation is made.
3. A person engaged in watching; a sentinel; a sentry.
4. Object or duty of forethought and care; responsibility.
on the lookout for in search of; looking for.
Moby Thesaurus II by Grady Ward, 1.0:
45 Moby Thesaurus words for "on the lookout for":
after, agape, agog, all agog, anticipant, anticipating,
anticipative, anticipatory, awaiting, certain, confident, delving,
digging, eager, expectant, expecting, fishing, forearmed,
forestalling, forewarned, gaping, hopeful, in anticipation,
in expectation, in search of, loaded for bear, looking for,
looking forward to, nosy, not surprised, optimistic, out for,
out for bear, poking, prepared, probing, prying, ready, sanguine,
searching, sure, unsurprised, waiting, waiting for, watching for