Compressed word forms, e.g. the Llyfr Coch Hergest Metrical Codes , an example of early cynghanedd (the basic concept of sound-arrangement within one line, using stress, alliteration and rhyme) described/translated here in English : 

billet spied
bolt sped
across field
crows fled
aloft, wounded
left one dead

the ss in across and the s of crows , which has a z sound corresponds 

Another interesting example of ‘compressed word forms’ are Kennings. Some I’m particularly fond of : 

gold
seeds of the Fyris Wolds , serpent’s lair , Sif’s hair (Derived from the story of when Loki cut off Sif’s hair. In order to amend his crime, Loki had the dwarf Dvalin make new hair for Sif, a wig of gold that grew like normal hair)

gold, sometimes amber
Freyja’s tearsDerived from the story of when Freyja could not find Óðr, her husband, the tears she shed were gold, and the trees which her tears fell upon were transmuted into amber.

the sea : whale-road

waves : Ægir’s daughters Egir had nine daughters called billow maidens who were personifications of the waves.

wind :breaker of trees