'smoothly-connected' originates from the combination of 'smoothly' and 'connected', where 'smoothly' is derived from 'smooth', meaning 'even or without roughness', and 'connected' from 'connect', meaning 'to join or link together'.

'smoothly' evolved from the Old English word 'smōð', and 'connected' from the Latin 'connectere', which became 'connect' in Middle English.

Initially, 'smoothly' meant 'without roughness', and 'connected' meant 'joined together'. Over time, the combined term 'smoothly-connected' came to describe a seamless linkage.