Střechýl is a regionalism unknown to most people, but still somehow comprehensible to everyone because it's clearly based on the word střecha (= roof).
Rampouch is the 19th century codification for icicle. It's based on old Czech form ropúch/ropuch which was a generic word for extension/protrusion. Right before the codification there was no word for icicle used nationwide, just multitude of various regionalisms including several cognate to rampouch, most notably rampúch. In addition, practically everyone was familiar with some word based on ropúch used in a different meaning. That's why rampouch was chosen by the codifers. (Older form rampúch was discarded because the ú-sound was obsolete.)
As for the other meanings of rampouch, they were mostly forgotten by general population, but sometimes accidentally reinvented as figurative comparision to icicle (e.g. dripstone or snot). One of the most common historical meanings was a tassel on flags/banners (still used in vexillology or as historicism in novels). Another usage is for a secondary branch on antler - this is the actual scientific term but also hunting slang (as hunting slang, střechýl is also attested for this meaning).
Sopel is another related word. It means snot in modern Standard Czech, but it means icicle in Standard Polish and some Czech dialects including some not closely related to Polish.