What do we think their secret code words might be?
1. (land, locale, sea): area, location, map, district?
2. (green, tree): plant, vegetable, forest, natural?
3. (path, travel): route, move, destination?
4. (feeling, ACRONYM): ?
bitter: I suppose if code word 4 is sour, this might fit 4 - but SOUR (Specific Oxygen Uptake Rate) isn't a well-known acronym (at least I didn't know it till I googled).
gum: some gum is green and gum comes from trees so 2? (I know, I'm not convinced either).
graveyard: if I go with my choices for bitter and gum, I have to choose between 1 and 3. I suppose 'destination' fits both path and travel, and as our ultimate destination is (usually) the graveyard, I'd choose 3 rather than 1.
So it's really no better than a wild ass guess, but I've come up with 4 2 3