The 3-letter sets below can become three 11-letter words by combining them, with a certain letter used as a connector. The same letter will be used to connect the words in each set; each set uses a different letter. Don’t change the order of the letters.

-1. ate, ate, boi, erp, gul, ibi, ist, ity, phi
2. arm, ben, end, int, nce, nts, rse, rsp, vol
3. cea, ele, ity, mon, sly, ter, toa, tma, tro
4. acr, bit, cal, inh, mon, ons, ous, pur, tan
5. cap, dis, ful, gas, ing, iva, omy, rec, rus

1. (L) boilerplate - gullibility - philatelist

That's how it's done!