Archaic second-person singular simple past form of begin(verb)
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Use "beganst" in a sentence
"What is youth, but an untamed beast? all whose actions are rash and rude, not capable of good counsel, when it is given; and, ape-like, delighting in nothing but in toys and babies? therefore thou no sooner beganst to have a little strength and discretion, but forthwith thou wast kept under the rod, and fear of parents and masters; as if thou hadst been born to live under the discipline of others, rather than at the disposition of thine own will."
"41 The woman whom thou sawest mourning, thou beganst to comfort her."
"49 And behold, thou hast seene the similitude of her: and because she lamented her sonne, thou beganst to comfort her: and of these thinges that haue chanced, these were to be opened to thee."