Stoop, condescend, deign can mean to descend below the level (as in rank or dignity) where one belongs or thinks he belongs to do something.
Stoop implies a descent not only in rank or dignity but also, and more often, from a relatively high moral plane to a lower one; the term, therefore, can suggest disgraceful or shameful action.
Often the term implies a lowering of one’s standards (as of conduct) or a debasement of one’s principles for some unworthy end (as to satisfy greed or ambition).
Condescend may imply the stooping of one who is actually exalted in power, rank, or dignity so as to accommodate himself to intercourse with those who are his inferiors; in this sense the term usually suggests graciousness and courtesy and a waiving of formalities.
Often, however, the term implies an assumption of superiority and a patronizing manner that tends to offend or affront the person who is regarded as an inferior.
Deign implies a temperament or frame of mind that makes one haughty, arrogant, or contemptuous more often than it implies high rank or dignity or high standards of conduct; it usually means to stoop to what one believes is not fully in keeping with one’s dignity or to something that one is reluctant to do or say or offer; therefore the term is most common with scarcely , hardly , or in negative constructions.