The answer to this riddle is a single English word.
Likely you'll find me when lending support
Or shedding some knots by a slip of some sort
Or adding the silver before fitting the frame
Keep calm and breathe is the key to this game.
If you have doubts about your answer, it is not correct.
question_asker was absolutely right. The the second line is boaty.
The answer is a very common English word. The clues refer to less common meanings of this word. Nothing really obscure, but definitely not the most common meanings.
Trust the last line.
Trust the title.
Trust me to be a pain in the posterior.