In the first section the poet describes a terrific wave in the ocean off Spain, comparing it to a rampart, a wound, a dragon, a mountain, the sea's brain, and "yeast for the ale that the whales brew".
"The Wave" is one of a group of three cywyddau by Gruffudd Gryg relating to his pilgrimage by sea to the shrine of St James at Santiago de Compostella.
The other two are an address to the moon reproaching it for causing a storm at sea on his outward journey, and a nostalgic description of the island of Anglesey, written in Spain.
This was interpreted by Ifor Williams and Thomas Roberts as meaning England under the rule of Henry IV, whose accession in 1399 would on this reading mark the earliest date the poems could have been written.
[7] "The Wave" is a poem expressing Gruffudd's homesickness as, on board a ship in a Spanish harbour, he awaits favourable weather for his return journey.
It involves a lengthy passage of dyfalu, description by the use of many far-fetched and imaginative metaphors and images, which might be seen as the main purpose of the poem;[10] the poet expresses both admiration and fear of the wave, turning in the dialogue section into comic deference when he realizes that it has come from his lady.
[10] She is described in other poems by Gruffudd as having eyes the colour of a ripe berry or a cow, coral and gold cheeks, a neck whiter than a swan or a seagull, and a fine mouth which delivers wise words.
[19] Rachel Bromwich was of the opinion that "The Wave" was one of "a handful of highly original and exceptional cywyddau which deserve to be placed on a par with Dafydd's finest work".