I am completely stuck on 143 down - Cheerful (5 letters). I have R?A?T and am pretty sure of the H (from142 across "Clock-making science" = HOROLOGY) and the A (from 158 across "Becomes tedious" = DRAGS). Not so sure about the T (from 166 across"Resourcefulness" = WITS. Would much apprerciate any suggestions.
Sorry, I should have said "R" instead of "H" so RIANT it is. Quite rare - it is in the Farlex Free Dictionary referred to by Mazie but I can't find it in the convenional Oxford and Chambers dictionaries I usually use - but these are the concise versions. The Farlex Free looks very useful. Many thanks to you all.