without reservation; freely; frankly
Used when encouraging someone to act without hesitation or restraint, often in offers or invitations.
Please help yourself without reservation.
Please feel free to give your opinion.
If you have any questions, please feel free to ask.
She's the type who says exactly what she thinks, without holding back.
Please feel free to use this computer.
気軽に emphasizes doing something casually and lightly without a big fuss, whereas 遠慮なく focuses on dropping polite hesitation toward another person.
遠慮なく means 'without hesitation/reserve' and can be neutral or even polite in invitation contexts, while ズケズケ specifically describes speech that feels rude or insensitive.
遠慮 is the plain noun/suru-verb meaning 'reserve, restraint,' while 遠慮なく is its adverbial form meaning 'without reserve' and cannot itself take する.
Adverbial form of 遠慮 (reserve, restraint) with なく (adverbial form of ない), literally 'without reserve'.