The most common and most likely answer to this crossword clue is the 7 letter word DECAPOD
I've seen this crossword clue in The Guardian
D
E
C
A
P
O
D
Buddy explains!
The straight part
We know that "lobster for one" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lobster for one = decapod.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DECAPOD mean?
DECAPOD noun- Any of various animals having ten legs or similar appendages, especially mollusks such as squid and cuttlefish.
- Any crustacean, of the order Decapoda, such as crabs or lobsters.
- A nickname for either the 0-10-0 or 2-10-0 train configurations. Sometimes capitalized.
- Having ten legs.