sag verb
ADV. slightly | wearily | back, forward He sagged wearily back in his chair. Helga's body sagged forward.
PREP. against She sagged against the door. | under The shelf sagged under the weight of hundreds of volumes.
PHRASES sag in the middle a mattress that was beginning to sag in the middle
You can also check other dicts: sag (English, 中文解释 ), wordnet sense, Collins Definition