(noun)
a decorative element or additional accessory that is added to something, especially clothing, or (informal) a traditional garnishing or accompaniment to a dish, meal, or special occasion;
e.g. The coat had a fur trimming around the edge of the hood. Mashed potatoes are my favorite trimming of a Thanksgiving dinner.
(noun)
the action of cutting away parts of something to make it the required shape or size or to make it neat;
e.g. He continued with his trimming of the bushes, humming a song as he worked.
(verb)
cutting away parts of something in order to make it the required shape or size or to make it neat, or broadly, removing the unwanted, unnecessary, or irregular parts from something;
e.g. She was trimming away the dead branches from the potted plants. He tried trimming the crusts off the sandwiches.
(verb)
adding decorative elements to something, typically in the form of pieces made of different materials or other contrasting items;
e.g. They were trimming the sleeves of the blouse with velvet cuffs as one of the final steps of its making.