Sentence:  A <WSD>Weak Verb</WSD> adds "d", "ed", or "t", to the Present Tense, to make the Past Tense; as, "invite", "invited"; "betray", "betrayed"; "step", "stept". 
Meaning of the word marked with <WSD> tags:  One of a class of Germanic verbs which use a dental affix appended to the stem to indicate tense; a Germanic weak verb.