The most common and most likely answer to this crossword clue is the 8 letter word SUCKLING
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result SUCKLING
Buddy explains!
The straight part
We know that "Cavalier poet/infant still at mother’s breast" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cavalier poet/infant still at mother’s breast = suckling.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 SUCKLING mean?
SUCKLING noun- An infant that is still being breastfed (being suckled) by its mother.
- A young mammal not yet weaned and still being fed milk by its mother.
- To give suck to; to nurse at the breast, udder, or dugs.
- To nurse; to suck milk from a nursing mother.
- To nurse from (a breast, nursing mother, etc.).