In a manner that lacks a front; in a way that is without forward-facing structure or appearance.
From 'frontless' (adjective) + '-ly' (adverb marker). This is a rare adverbial formation following standard English patterns.
Most '-less' words can take the '-ly' adverb suffix, but adding '-ly' to already negative adjectives like 'frontlessly' creates awkward double-negatives that English speakers instinctively avoid, which is why such words feel forced.
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