'tightly-bound' originates from the combination of 'tight' and 'bound', where 'tight' comes from Old English 'thight' meaning 'dense, solid' and 'bound' from Old English 'bindan' meaning 'to tie or fasten'.

'tight' changed from Old English 'thight' to Middle English 'tight' and 'bound' from Old English 'bindan' to Middle English 'bounden', eventually forming the modern English 'tightly-bound'.

Initially, 'tight' meant 'dense or solid', and 'bound' meant 'to tie or fasten', evolving into the current meaning of 'firmly or closely held together'.