The Hebrew verb ba'ash (H887) means to emit a foul odor, to stink, or figuratively to make oneself odious and offensive. It describes literal putrefaction as well as the moral stench of sin and covenant unfaithfulness.
Just as rotting flesh offends the nostrils, so sin and disobedience produce a spiritual stench before a holy God. Israel's idolatry is described as making themselves an abomination (ba'ash) before the LORD. Conversely, sacrificial worship produced a 'pleasing aroma' — the opposite of ba'ash. This imagery underscores that worship and obedience please God while rebellion is genuinely repulsive to His holiness.