Each of the answers to the clues below contains two or three words which differ only by the same single letter.What letter is it, and what are the words?

1. Ghostly anger
2. Porta-Potty
3. Trickier basketball player
4. French bricklayer
5. Farmer who wants to irrigate - at times
6. Twisting paths of corn

Answers:

The letter is I - dropped form one of the words of each answer to spell the second (and third) words:

1. WRAITH WRATH
2. TOILET TO LET
3. CAGIER CAGER
4. MAISON MASON
5. WATER WAITER
6. MAIZE MAZE