Without flirtation; lacking any element of flirting or romantic playfulness.
From 'flirtation' plus the suffix '-less' (meaning 'without'). This is a deliberate opposite formation, like 'fearless' from 'fear.'
The '-less' suffix is one of English's most productive tools for creating opposites, but 'flirtationless' reveals something: we rarely use it because in real life, most interactions are somewhat flirtatious—the absence is so common it doesn't need naming.
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