In a manner characteristic of or resembling a groom; in the manner described by groomish.
From groomish plus the adverbial suffix -ly, which converts adjectives into adverbs describing how something is done.
Adding -ly to -ish words feels redundant ('groomishly'), which is why you almost never see this combination—English speakers naturally avoid stacking suffixes this way.
Complete word intelligence in one call. Free tier — 50 lookups/day.