The most common and most likely answer to this crossword clue is the 10 letter word MAIDENHAIR
I've seen this crossword clue in The Times
M
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The straight part
We know that "House plant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case house plant = maidenhair.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 MAIDENHAIR mean?
MAIDENHAIR noun- A woman's pubic hair
- Either of two species of genus Adiantum of fern with delicate, hair-like stalks, especially Adiantum capillus-veneris
- Designating various types of moss or flowering plants.
- Either of two ericaceous plants, the creeping snowberry or the checkerberry.