There are ten definitions below. The answer to the first definition is one letter; the answer to each of the definitions from two onwards is an anagram of the previous answer with one letter added. So SPOT could be followed by POSIT; that is, SPOT + I rearranged.

1. Indefinite article
2. Father
3. Short sleep
4. Severe ache
5. Inappropriate
6. Decorates
7. Otter’s dung (Singular)
8. Larders
9. Soaked by a downpour
10. Gender neutral term for a restaurant server