Just for fun, I did a CELT search for 'loiscend' (frog) with various spellings.
I found a few things. Looks like a compound of 'los' ("end, butt, foot, point of
a staff, stick, etc....stem of a drinking horn...tail..") and 'cenn' (head). Liz
1. From 'The Voyage of the Hui Corra' (CELT says 11th century)
'Rochonnac tra cetre srotha an ifirn .i. sruth loiscenn & sruth naithrech & sruth
teneadh & sruth snechta.' (My translation -- he saw then the four streams of
hell, that is, a stream of frogs and a stream of snakes and a stream of fire
and a stream of snow.)
2. From Togail na Tebe (Celt dates it 15th century)
"Conid immi sin darigni Ulcan in set sirbhuan sonashercach sin re silliud sechtair
fair co nemib nathrach, co lingur loiscend, co salchar slama
tened & saignen, co mongaib dubglasa duaibsecha dracon, co leccaib
lasamna loiscthecha ar medon and."
I wonder if the phrase "co nemib nathrach, co lingur loiscend, co salchar
slama", which has 5 syllables in each part and alliteration, was taken from a
poem. The sentence is loaded with alliteration.
3. It shows up in a list of animals (mostly animals not found in Ireland) in Cath
Catharda (CELT gives a date range of 900 to 1200) -
'Cidh fil ann tra acht cach anmanna isin domun uile doneoch
ercoitiges do duine, eter leoman & mathgaman & loiscenn
& tigir & viper & colubir & nathir neimide arcena, '
4. Two people with the name 'Loiscenn' show up in genealogies in Rawlinson