stagnate
staɡˈneɪt,ˈstaɡneɪt/
verb
gerund or present participle: stagnating
(of water or air) cease to flow or move; become stagnant.
synonyms: stop flowing, become stagnant, become trapped; More
cease developing; become inactive or dull.
"teaching can easily stagnate into a set of routines"
synonyms: become stagnant, do nothing, stand still, be sluggish, lie dormant, be inert, languish, decline, deteriorate, fall
"imports rose while exports stagnated"