Crossword Clue:

that cannot be ridden also UNRIDEABLE

AnswerCrossword Clue
LLAMAAnimal that can be ridden
SINEWave that can't be ridden
LAMELike a horse that can no longer be ridden
INDELIBLEThat cannot be forgotten
TRESSLock that cannot be opened
DRAFTCall to arms (that cannot be denied).