In an ambidextrous manner; with equal skill using both hands, or with clever adaptability in handling situations.
From ambidexterous + -ly, a standard English adverb formation. The -ly suffix transforms the adjective into an adverb describing how an action is performed.
Adding -ly to adjectives to make adverbs is one of English's most productive word-building patterns—you can theoretically add it to almost any adjective, which is why older texts sometimes have forgotten adverbs that sound completely new.
Complete word intelligence in one call. Free tier — 50 lookups/day.