Left speech radical - the indexing component. Marks 谎 as a word about speaking, in this case false speaking. The same radical sits in 说 (say), 话 (speech), 语 (language), 谣 (rumor), 诈 (deceive).
Right 荒 supplies the sound huǎng (drifted in tone from huāng) and adds a hint of meaning - wild, absurd, unfounded. Speech that is wild and unfounded is exactly what a lie is, making this a tidy phono-semantic pair.
